1. Field of the Invention
The present invention relates generally to the field of propulsion systems for watercraft, such as pleasure craft, fishing boats, pontoon boats, ski boats, and so forth. More particularly, the invention relates to a propulsion system that includes an inboard electric motor drive unit and an outboard propulsion unit or prop.
2. Description of the Related Art
In the field of propulsion systems for watercraft, and particularly for pleasure craft, various approaches have been proposed and adopted for use. In general, such systems include internal combustion engines drives or electric drives. Internal combustion engine drives, in turn, include both outboard motors, which are typically secured to a transom of a boat, and inboard motors which position an internal combustion engine within a housing or compartment of the hull, with a propeller extending through the transom. Both outboard and inboard motors are particularly useful for high-speed and highly responsive navigation of the watercraft. Drawbacks of such drives, however, include their noise levels, exhaust emissions, relative complexity, size, and weight.
Electric propulsion systems for pleasure craft are typically referred to as trolling motors or electric outboards. These systems include an electric motor which can be rotated at various speeds to drive a prop. The prop produces a thrust which is directed by proper orientation of the propulsion unit. In conventional trolling motors, for example, a control head may be manually oriented to navigate the boat in a desired direction, or a remote control assembly may be provided for rotating a support tube which holds the propulsion unit submerged during use. While certain relatively minor differences may exist, the term electric outboard is typically employed for the conventional trolling motor design, but with a horsepower range elevated with respect to the conventional trolling motor, such as in excess of 1 horsepower.
While the conventional trolling motor provides quiet and reliable navigation, extremely useful for certain activities such as fishing, drawbacks of the conventional design do exist. For example, conventional trolling motors are designed as add-on units which are typically supported by a mounting structure on the deck of a boat. The mounting structure, a wide range of which may be obtained commercially, often allow for relatively straightforward deployment of the motor to position the propulsion unit below the waterline, and retraction of the unit for stowage. The entire motor and mount, however, generally remain securely fixed to the deck, both during use and when stowed. The resulting structure is somewhat cumbersome and occupies useful space on the deck, limiting access to the water in the area of the motor mount. Moreover, while much energy and creativity have been invested in boat designs, the aesthetics and aerodynamics of the hull may be somewhat impaired by the trolling motor and mount positioned on the deck, typically on or adjacent to the bow.
In addition to the foregoing drawbacks, conventional trolling motors and electric outboards are somewhat prone to damage, and require special packaging and mounting structures. For example, if the motor strikes a submerged object, significant damage can occur, particularly to the propulsion unit, to the motor support tube, and to the entire mounting structure. Mounts have been devised, therefore, to limit the risk of such damage. However, damage can still occur, particularly when navigating through shallow waters where submerged objects are likely to be found. Moreover, due to the submersion of the electric motor itself in the propulsion unit of conventional trolling motors, a sealed housing must be provided for isolating the interior cavity in which the motor is placed from the surrounding water. The housing must be able to withstand not only the environment of its normal operation, but must stand up to contact with the submerged objects, and so forth. Similarly, when in the stowed position, the weight of the electric motor itself, typically the heaviest part of the assembly, may result in damage due to vibration or bouncing during transport. Finally, whether controlled via signals conveyed through a wiring harness or through an RF connection, the electronics of the trolling motor are ultimately exposed to the elements and must be protected in sealed housings, both in the propulsion unit and in the motor head.
There is a need, therefore, for an improved trolling motor design which addresses the drawbacks of existing structures. There is a particular need for a design which can provide good navigational control, while eliminating the need to mount the motor on a boat deck and deploy it from the deck during use.
The invention provides a novel design for a trolling motor or electric propulsion drive designed to respond to these needs. The design is based upon an electric drive system, including a variable speed electric motor positioned within a cavity of a boat hull. The electric motor is drivingly coupled to a prop which is disposed outboard of the hull shell. A drive assembly extends between the motor and the prop for transmission of torque during operation. The power transmission assembly may include support components for fixing both the electric motor and the prop to the hull, and for maintaining a seal at a location where the transmission components extend through the hull.
The inventive design may be adapted for a wide variety of configurations and uses. For example, in a present embodiment, the design may be adapted to be mounted in any desired region of the boat. In one embodiment, for example, the drive is positioned near a stern region of a boat such that the electric motor is positioned within a cavity accessible from the cabin or deck, but remains generally unseen and protected during use. Alternative designs may provide for locating the system at other positions on the boat, such as forward of the transverse centerline of the boat, as in a bow thruster position. Wiring may be provided entirely below deck and routed to control units or circuitry where commands originate. The power transmission drive train extends through the hull to drive the prop. While the entire assembly, or the prop alone, may be angularly positionable to orient the thrust in a desired direction, the assembly may be fixed in position, and resultant thrust provided by cooperation of two or more such units. The design thus allows for the propulsion system to be completely removed from the boat deck, both during use and stowage.